HYDRAULIC PRESSURE DRIVING DEVICE FOR HYDRAULIC SHOVEL

摘要

PROBLEM TO BE SOLVED: To perform a fast starting of self-weight descent of a boom irrespective of any working posture of a hydraulic shovel when the boom held in air is started to descend.SOLUTION: This invention comprises a jack-up changing-over valve 25 changed over when a bottom pressure of a boom 5 reaches to a set pressure; a flow passage changing part for changing a flow passage of hydraulic oil supplied to a meter-in part of a boom direction control valve 22 as this jack-up changing-over valve 25 is changed over to an opened passage side or a closed passage side; a fast operation detecting part including a function setting part 51d etc. of a controller 51 for detecting that the boom direction control valve 22 is rapidly operated when a retracting operation for a boom cylinder 11 for descending the boom 5 held in air is started; and a changing control part including a proportional solenoid valve 52 and a control valve 53 etc. for performing a control operation for changing-over the jack-up changing-over valve 25 when the fast operation is detected and for changing a flow passage changing part including a flow rate control valve 26 etc. to the opened passage side for a prescribed period of time.